The present invention relates to a rotatory pump, as well as to an impeller wheel for a rotatory pump.
Using rotatory pumps, media or fluids of the most various kinds can be conveyed. These may be gases, flowable solids and liquids, as well as liquids containing solid components and/or fibers.
The pump efficiency of rotatory pumps is determined substantially by the impeller wheel. Good efficiencies may be obtained with impeller wheels having a front cover disk facing the incoming fluid to be conveyed, as well as a rear cover disk facing away from the incoming fluid to be conveyed, with blades or ribs disposed between them. Impeller wheels of this kind are fabricated integrally as finished castings. Because the ribs or blades extend radially outwards along an arc from their footings on the hub of the impeller wheel, impeller wheels of this kind may be cast only by using cores, this rendering the fabrication outlay and therewith the cost of such an impeller wheel correspondingly high.
Furthermore, with housings in the form of castings, the inner wall portions facing the impeller wheels must be machined in order, on the one hand, to create a space for the rotary movement of the impeller wheel, and on the other hand, to establish a seating for the annular gap. This also is labour-consuming and therefore costly.
When closed impeller wheels of this kind are used for conveying fluids containing solid materials or solid bodies, there is a danger of the flow passages formed by the blades and the front and rear cover disk becoming damaged or even blocked.
For this reason, impeller wheels without a front cover disk also are to be found in practice, these being termed non-chokable wheels. With impeller wheels of this kind, the flow channel needed for guiding the fluid to be conveyed is formed by the rear cover disk, the blades disposed thereon, and the housing inner wall portions facing the blades. Because there is no front cover disk, impeller wheels of this kind may be fabricated relatively easily and therefore inexpensively. However, rotatory pumps containing impeller wheels of this kind exhibit a markedly worse efficiency than rotatory pumps having closed impeller wheels.
It is the object of the present invention to produce a rotatory pump which has an impeller wheel that can be simply fabricated and which is of high efficiency. Furthermore, it is the object of the present invention to fabricate a suitable impeller wheel therefor.
The above object is achieved by the features claimed in the appended claims as far as the rotatory pump is concerned. Advantageous developments of this rotatory pump are also claimed.
Owing to the provision of the raised portions or knobs or bulges, the possibility is given of an impeller wheel formed without a front cover disk being disposed so closely to the inner wall portions of the housing that a structure is created which is similar to a closed impeller wheel. However, because there is no front cover disk, the impeller wheel for the rotatory pump of the invention may be fabricated far more easily and therefore at more favorable cost. By means of suitable trials it was possible to show that the rotatory pump of the invention is of an efficiency which is equal to or even higher than that of a rotatory pump having a closed impeller wheel at the same driving power and with the same fluid to be conveyed. For this, an unusual approach, that of the impeller wheel contacting the inner wall portions of the housing, has been adopted. In this, by means of the raised portions an at least point-shaped or line-shaped contact is established between the impeller wheel of the rotatory pump and the inner wall portions of the housing. Following a relatively short running-in period, contact lines or contact faces which are hydraulically smooth form on the raised portions and on the runner groove worked into the inner wall portions of the housing. The fluid to be conveyed then forms a lubricating film between the contact regions, so that the frictional resistance as well as the noise generation of the rotatory pump of the invention does not exceed that of a rotatory pump with a closed impeller wheel.
In principle, the raised portions may be fitted to the blades of the disk or the rear cover disk after the fabrication of the impeller wheel. However, a particularly simple and therefore cost-advantageous manufacture of the raised portions may be achieved by the raised portions being integrally formed onto the blades, so that they may be cast together with the impeller wheel in the casting operation.
In principle, the raised portions may be of any desired shape. However, in order to facilitate the formation of the groove in the inner wall portions of the housing, it is of advantage for the cross-sections of the raised portions, as seen in a longitudinal section, i.e. parallel to the shaft axis, to be of the shape a segment of a circle.
The raised portions may be disposed on the blades at any desired value of the radius. It has been shown to be of particular advantage for each of the raised portions to be disposed approximately in a region at the mid-radius position of a blade.
In order to ensure a reliable contact of the raised portions with the inner wall portions of the housing even after the running-in phase, it is of advantage for the fitting clearance of the disk on the driving shaft to be smaller than the height of the raised portions, as measured along the axial direction of the driving shafts.
In principle, in the case of a plurality of raised portions, these may be disposed at different radial distances along the respective blade. However, in order to keep the frictional resistance low, in particular during the running-in period, it is of advantage for the raised portions to be disposed on the blades to lie in a circle concentric with the axis of the driving shaft at equal spacings, in particular of 120xc2x0.
Furthermore, if the housing is fabricated as a casting, it has been shown to be of advantage for at least the inner wall portions of the housing facing the blades to be not machined. This ensures, by making use of the hard cast skin, that the raised portions do not penetrate too deeply and that bearing faces of sufficient hardness are formed, so that uniform running of the impeller wheel is ensured.
Furthermore, in order to ensure that the raised portions bear in a defined manner against the inner wall portions of the housing which face the blades, a biasing or adjusting device may be provided, by means of which the raised portions may be urged against the inner wall portions of the housing which face the blades.
In this case, in order to ensure a compact construction and a simple assembly, the biasing or adjusting device may be disposed on the driving shaft on that side of the disk which faces away from the blades. If the biasing or adjusting device is disposed on that side of the cover disk which faces the blades, then there will result with the same structural components, in particular with the same impeller wheel, a second rotatory pump which, although the raised portions no longer bear against or contact the inner wall portions of the housing which face the blades to thus form narrow flow channels, may be used, for example for liquids with very large solid matter components, or even for solid materials, for example for conveying air- and gas-containing media as well as those which easily tend to cause choking. In the same way, a gentle conveying of solid matter particles, even of slightly abrasive components in the medium being conveyed, may be achieved with this rotatory pump. Thus, using the solution proposed by the invention, a xe2x80x9cbuilding block systemxe2x80x9d of different rotatory pumps may be established.
If the biasing or adjusting device is designed to be of spring-like elasticity, then it will be possible for the impeller wheel to reversibly give way along the axial direction when a penetration by solid matter occurs, so that damage to the blades and/or the inner wall portions of the housing which face the blades is prevented.
For this, the biasing or adjusting device may be constituted by mechanical components of the most various kinds. For example, the biasing or adjusting device may be formed by a metallic spring member, in particular a helical pressure spring, and particularly also a conical pressure spring or an annular member made of an elastomer, in particular rubber.
As far as the impeller wheel is concerned, the above object is achieved by the features claimed in the appended claims, including advantageous developments. The same advantages apply to the impeller wheel of the invention as have been set out initially in connection with the rotatory pump of the invention.